From Federal Republic of Germany Patent Specification No. 16 71 017, it is known to produce building materials with the addition of a resin based on an amino-s-triazine with at least two NH.sub.2 groups modified with sulphite or sulphonic acid. The sulphonic acid-modified melamine or guanamine resins thereby used can only be produced with a solids content of up to about 20% by weight and have a relatively high content of free formaldehyde.
Condensation products of this type with a high solids content of up to 50% by weight can be produced according to the processes described in South African Patent Specification No. 78/2022, as well as in Federal Republic of Germany Patent Specification No. 23 59 291 but the content of free formaldehyde of these melamine-formaldehyde condensation products remains unchangedly high.
This applies to the condensation products which, according to Federal Republic of Germany Patent Specification No. 25 05 587, also have an additional content of urea, as well as to the products according to Federal Republic of Germany Patent Specification No. 31 07 852 for the production of which there are also used relatively expensive amino and carboxylic acids in order to adjust the necessary pH value. The latter appears to be problematical, especially from the economic point of view.
In principle, it is, naturally, possible to reduce the content of free formaldehyde of these resins by the subsequent addition of a formaldehyde receiver, for example one based on urea or a urea derivative. However, in this way, foreign materials get into the condensation product, which is undesirable for many fields of use because the quality of the product can thereby be negatively influenced. Furthermore, this subsequent treatment represents an additional treatment step which requires additional operational and investment costs and is, therefore, economically problematical.